a) Field of the Invention
The present invention relates to an improvement in an optical system which is included in a photographic system, a view finder system, automatic exposure control system, an automatic focusing auxiliary light illumination system or the like for an image pickup apparatus such as a film camera, a digital camera, a video camera or the like.
b) Description of the Prior Art
Demands for thinner configurations of image pickup apparatuses such as film cameras, digital cameras, video cameras and the like become higher and higher year by year. It is therefore important to shorten total lengths of optical systems such as photographic optical systems and view finder optical systems to be used in the image pickup apparatuses.
Since there lies a limit in shortening a total length of such an optical system by reducing a number of compositional lens elements, it is attempted to shorten a total length by bending an optical system using a mirror.
For bending an optical system, however, it is necessary to reserve a space for a bent portion, and a space for moving lens units in a zoom optical system or moving lens unit(s) for focusing in particular is apt to be insufficient, thereby making it difficult to obtain a required zoom ratio and shorten an extremely short distance. In case of a view finder, it is difficult to shorten a total length since a space must be reserved for moving a lens unit to adjust or correct diopter.
Furthermore, it is desirable for automatic exposure control of an image pickup apparatus to make variable a weighted coefficient distribution for the so-called weighted mean light measurement according to a program of what portion of a photographing range of an object is to be considered at what ratio. There are adopted, for example, a center weighted mean light measurement, spot light measurement and the like. For carrying out such a variable weighted mean light measurement, it is effective to change a focus point location of a condenser lens component which condenses rays on a sensor. In such a case, it is necessary to use a mechanism which changes a relative positional relation between the condenser lens component and the sensor, thereby complicating an image pickup apparatus.
On the other hand, zoom lens systems nowadays constitute a main current of photographic optical systems for image pickup apparatuses and when an exclusive condenser optical system has a single focal point, a light measuring area is changed relative to a photographing range of an object by zooming, whereby the center weighted mean light measurement at a wide position may be a mean light measurement at a tele position. In such a case, a condenser lens component which condenses rays on a sensor in a light measuring system must have a vari-focal function. When the condenser lens has the vari-focal function, however, a magnification changing mechanism of the light measuring system is complicated and when the condenser lens component is interlocked with a zoom lens system of a photographic system, the mechanism is more complicated.
Digital cameras (electronic cameras) have recently been attracting attention as cameras of a next generation which are to substitute for silver salt 35 mm film cameras (Leica camera by popular name).
An effective image pickup surface of an image pickup device generally used for a digital camera has a size which is much smaller than that of a silver salt film. Therefore, the image pickup device has defect that it has too large a depth of field can hardly provide an effect of defocus. In contrast, there is a case where pan-focus is desired.
In order to realize these effects, there is conceivable a method to carry out an image processing so as to change an apparent depth of field by composing image data of an identical scene having focus points which are different little by little. In such a case, however, it is necessary to obtain a plurality of image data in a short time and at a high speed while changing a focus point.
It is therefore necessary to contrive optical systems at respective portions of an image pickup apparatus such as a camera, thereby not only thinning a photographic system, a view finder system, a light measuring system, a range finding system at the respective portions but also enhancing performance of these systems.
In other words, it is necessary to configure the photographic system so as to exhibit predetermined performance of use even when an optical path is bent, remove a moving space for diopter adjustment in the view finder system, configure the light measuring system without complicating a mechanism so as to be capable of changing a focal length of a condense lens having a simple composition so as to make variable a weight coefficient distribution for the weighted mean light measurement according to a program of what portion of a photographic range of an object is to be considered at what degree.
The light measuring system is configured so as to be capable of changing a focal length of a condenser lens system in order to change a distribution of weight coefficients in accordance with a magnification change of the photographic optical system.
Furthermore, it is necessary to configure the light measuring system so as to be capable of obtaining desired distributions of weight coefficients from a wide position to a tele position in conjunction with a magnification change of a zoom lens system.
Furthermore, a light projector optical system of the range finding system is configured so as to have a simple composition without complicating a mechanism and be capable of changing a magnification of the light projector optical system in conjunction with a magnification of the photographic optical system, and optimalizing a range finding region from the wide position to the tele position.
Furthermore, it is necessary to obtain means for obtaining an image on which defocuses before and after a focus point are emphasized by reducing an apparent depth of field of an image photographed with an image pickup apparatus which uses an image pickup device having a small effective image pickup surface size.